The invention relates to a method for detecting X-rays where the individual energy ranges are simultaneously radiated onto an object to be X-rayed and are thereby weakened and, the weakened X-ray beams are separated into a low-energy range and a high-energy range. The invention additionally relates to an arrangement for implementing this method.
It is known to use a detection device, configured with several detector pairs, for the detection and determination of materials with the aid of X-rays. Each detector pair consists of one 0.1-0.5 mm thin and one 0.5-20 mm thick radiation detector. The radiation detectors are arranged one after another and are therefore penetrated successively by the X-rays or the roentgen quanta from a radiation source. The X-ray beam consequently is separated into individual energy ranges, which is necessary to determine the material types of a good examined with the aid of X-rays. The fact that photons with higher energy show little interaction in the thin detector, in the following called a low-detector, and are thus absorbed in the subsequent thick detector, in the following called a high detector, is used for the separation of the radiation into different energy ranges. In contrast, photons with low energy are absorbed almost completely in the low detector. The radiation impinging on the detector pairs changes as a result of the good or material to be tested, which is located between the radiation source and the detection device. Based on the change in the signals of each detector pair, it is then possible to draw conclusions as to the materials inserted into the ray path.
Since a certain interaction of the high-energetic photons in the low detector cannot be prevented, high-energy shares of the impinging radiation are also absorbed. As a result, an overlapping of the energy ranges occurs. Consequently, these traditional arrangements are not suitable for an exact material determination.
British patent reference GB-1154973 discloses a detector arrangement for taking an X-ray of a human body. In that case, a respective one filter is arranged between three X-ray films. Bones, muscles and fatty tissues are shown on the first X-ray film. The following first filter is dimensioned such that it filters out the energy shares of the bones so that only the energy shares of the muscles and the fatty tissue are shown on the second X-ray film. Subsequently, the energy shares for the fat or fatty tissue are filtered out in the second filter, so that only the energy shares for the muscles are captured on the third X-ray film. The X-ray picture is then composed of the image on the first X-ray film less the images from both the second and third X-ray films. For this, the first X-ray film is a film positive and the other two films are respectively film negatives. The resulting X-ray image represents the bone information.
U.S. Pat. No. 4,626,688 discloses a separated energy radiation detection with varied energy levels, which are generated and transmitted with a time displacement. Thus, a low frequency radiation is initially produced and is beamed through the body of a patient. A first detector absorbs this radiation and transmits the signals, resulting from the energy spectra, to a digital processor circuit. Subsequently, a higher frequency is generated and is beamed as radiation with higher energy through the patient and is then transmitted to the processor via a second detector. In the processor, the low frequency is subtracted from the high frequency, so that the low energy shares no longer form a component of the higher frequency. The higher frequency represents the bone information, as is known, so that the low energy shares of the soft body tissues are computed out of the high-energy shares through this measure. The image on a luminous screen again represents only the information on the X-rayed bones.
The disadvantage of the aforementioned arrangements and methods is that the energy ranges are reduced to an energy range that corresponds to the searched for material, so that the arrangements and methods can be used only if the materials and energy spectra to be detected are known ahead of time.
U.S. Pat. No. 4,029,963 discloses an arrangement and a method for detecting and identifying various materials. In this case, the transmitted X-rays are from the start separated into low-energy ranges and high-energy ranges, which are thus free of spectral displacements. A radiation depending on the atomic number Z, as well as a density-dependent radiation are determined from the separately transmitted rays through mathematical correlation. The radiation depending on the atomic number Z is proportional to the photoelectric component while the density-dependent radiation is proportional to the electrode density. The material is determined on the basis of this correlation.
It is the object of the invention to provide a method and an arrangement, which allow a clearer separation of low-energy shares and high-energy shares of a single X-ray beam. As a result, the X-rayed materials can be identified easier with only a single X-ray beam.